Radiation is a primary modality in cancer treatment. Radiation can also reduce tumor growth outside the treatment field, often referred to as the abscopal effect. The mechanisms and therapeutic potential of the abscopal effect have not been fully elucidated. We evaluated the role of vaccination directed against a tumor-associated antigen (TAA) in the induction and amplification of radiation induced abscopal effects. Active-specific immunotherapy with a TAA-specific vaccine regimen was used to induce and potentiate T-cell responses against carcinoembryonic antigen (CEA) in combination with local irradiation of subcutaneous tumors. We examined the potential synergy of a poxvirus-based CEA vaccine regimen in CEA-transgenic (Tg) mice in combination with either external beam radiation or brachytherapy of local tumors. The induction of CD8(+) T cells specific for multiple TAAs not encoded by the vaccine was observed after the combination therapy. In two tumor models, the antigen cascade responses induced by vaccine and local irradiation mediated the regression of antigen negative metastases at distal subcutaneous or pulmonary sites. Clinically, local control of the primary tumor is necessary and can sometimes prevent metastases; however, irradiation generally fails to control preexisting metastases. These studies suggest that by coupling tumor irradiation with immunotherapy, the abscopal effect can transcend from anecdotal observation to a defined mechanism that can be exploited for the treatment of systemic disease.The use of chelated radionuclide (Samarium-153-EDTMP) to modulate phenotype of tumor cells and enhance T-cell-mediated killing. Exposing human tumor cells to sublethal doses of external beam radiation upregulates expression of tumor antigen and accessory molecules, rendering tumor cells more susceptible to killing by antigen-specific cytotoxic T lymphocytes (CTLs). This project explored the possibility that exposure to palliative doses of a radiopharmaceutical agent could alter the phenotype of tumor cells to render them more susceptible to T-ell-mediated killing. Here, 10 human tumor cell lines (4 prostate, 2 breast, and 4 lung) were exposed to increasing doses of the radiopharmaceutical samarium-153-ethylenediaminetetramethylenephosphonate (153Sm-EDTMP) used in cancer patients to treat pain due to bone metastasis. Fluorescence-activated cell sorting analysis and quantitative real-time polymerase chain reaction (PCR) analysis for expression of five surface molecules and several tumor-associated antigens involved in prostate cancer were done. LNCaP human prostate cancer cells were exposed to153Sm-EDTMPand incubated with tumor-associated antigen-specific CTL in a CTL killing assay to determine whether exposure to 153Sm-EDTMP rendered LNCaP cells more susceptible to T-cell-mediated killing. Tumor cells up-regulated the surface molecules Fas (100% of cell lines upregulated Fas), carcinoembryonic antigen (90%), mucin-1 (60%), major histocompatibility complex (MHC) class I (50%), and intercellular adhesion molecule-1 (40%) in response to 153Sm-EDTMP. Quantitative real-time PCR analysis revealed additional upregulated tumor antigens. Exposure to 153Sm-EDTMP rendered LNCaP cells more susceptible to killing by CTLs specific for prostate-specific antigen, carcinoembryonic antigen (CEA), and mucin-1. Doses of 153Sm-EDTMP equivalent to palliative doses delivered to bone alter the phenotype of tumor cells, suggesting that 153Sm-EDTMP may work synergistically with immunotherapy to increase the susceptibility of tumor cells to CTL killing. Image-guided radiofrequency ablation (RFA) is a local regional therapy increasingly used to treat a broad spectrum of malignancies. However, relapse often occurs (&gt;15% for tumors &lt; 3 cm). Hyperthermia-induced cell death resulting from RFA tumor ablation is known to induce and /or augment anti-tumor immune responses. We sought to determine in a preclinical model if (a) RFA could positively modulate components of the immune system, and (b) could RFA be combined with vaccine immunotherapy to further increase antitumor activity and potentially prevent tumor relapse and / or treat more distant disease. We examined the effect of sub-lethal hyperthermia in-vitro on cell-surface phenotype and sensitivity to CTL-mediated killing of murine colon carcinoma cells expressing the tumor-associated antigen (TAA) CEA (MC38-CEA). We also evaluated the effect of RFA in-vivo on the phenotype of MC38-CEA tumors, and on the induction of tumor-specific immune responses. Finally, we evaluated the potential synergy between RFA and a recombinant viral vaccine expressing CEA and a TRIad of COstimulatory Molecules, CEA/TRICOM. These studies demonstrated that exposure of MC38-CEA cells in-vitro to sub-lethal hyperthermia increases cell-surface expression of CEA, HSP-70, and ICAM-1, and renders tumor cells more susceptible to CTL-mediated lysis. These studies also demonstrated that RFA of MC38-CEA tumors (a) induces upregulation of HSP-70 and ICAM-1 on the cell-surface of tumor cells, (b) increases splenic CD4+ and CD8+ T cell responses to CEA and to additional endogenous TAAs, including gp70, and (c) improves recruitment of CD8+ T cells to the tumor. Antitumor studies showed that RFA combined with vaccine eliminated primary MC38-CEA sc tumors and significantly controlled growth of distant disease.Taken together, these data indicate a potential clinical benefit in combining RFA with vaccine in patients with multiple tumor lesions to capitalize on the induction and expansion of diverse immune responses that may act on untreated distant metastases.